Gentlemen, Stop Your Engines: Greening Car Gizmos

As solar panels become smaller, more efficient, and cheaper, green innovators are developing more uses for them every day. It can seem like there’s a solar-powered version of almost every possible technology: phones, laptops, cars, planes, generators, attic fans, Christmas lights, and, of course, bikinis. Just because solar energy can power a device, though, doesn’t mean it makes sense to use it.

Consider cars, for example. Fifteen years ago, solar-powered cars were a novelty, a technology so unreliable that the main criteria for winning the World Solar Challenge race was finishing the course. Now, solar-powered cars can top 100 miles per hour and compete in a contest that actually resembles a race. Yet because of cost and logistical hurdles, they remain out of reach to most drivers. Solar power could serve a role in making the rest of our vehicles more energy-efficient, though—not by powering the engines, but all those other doohickeys inside our cars: Power steering, power locks, power windows, radios, iPod inputs, and—the biggest energy-guzzling appliance of all—air conditioning.

Solar-powered car air conditioning has been working its way toward the mainstream. In 2007, a designer developed a prototype for a solar-powered air conditioner that anyone could toss into their car. That same year, a team of researchers in Hong Kong developed a unit that could cool the cab of a truck but wasn’t particularly practical for consumer cars. This fall, the same group of partners came out with a system small and flexible enough to sit on the roof of any car. And since 2008, Toyota has been toying with solar-powered additions to the Prius—not only air conditioning, but also ventilation that keeps air flowing through the car while it’s parked.

Attaching solar power to an auxiliary function like air conditioning makes energy sense. A gas-powered engine can move a car down the road at 65 miles per hour without stressing itself, which means it’s more machine than is needed to keep the car cool while idling at a traffic light. Solar-powered air conditioning means cool air can blow out of the vents when the engine is off.

For conventional vehicles, solar-powered A/C can improve efficiency, as air conditioning trashes fuel economy. But for a hybrid car like the Prius, solar-powered air conditioning counts more toward green posturing than real energy savings. Even in older models, cars can run the air conditioning off the hybrid’s battery, which still uses power, but eliminates the additional environmental costs of manufacturing a mostly superfluous solar panel (not to mention the additional cost the car deal will tack on for that luxury). Rather than search for a new source of power, car manufacturers could simply start installing more efficient A/C units.

These options require designers are thinking more closely about which power sources can most efficiently power which parts of a vehicle. At its most extreme, this means fundamentally rethinking how cars are built: “Put an electric motor in each wheel, for instance, and suddenly there’s no need for a transmission, clutch, driveshaft, axles, universal joints, or differentials,” the Rocky Mountain Institute suggested in Reinventing Fire. Green design requires more subtle thinking than just slapping a solar panel on every device that can carry one.